Source: http://www.abarim-publications.com/Meaning/Ismachiah.html

🔼The name Ismachiah in the Bible

The name Ismachiah (or rather Ismachiahu) occurs only one time in the Bible. He is one of ten Levites who collect tithes and offerings from visitors of the Temple during the days of king Hezekiah's reorganization of the Temple services (2 Chronicles 31:13). Ismachiah and his colleagues operate under the authority of Conaniah and his assisting brother Shimei.

🔼Etymology of the name Ismachiah

The name Ismachiah consists of two elements. The final part is יה (Yah) = יהו (Yahu) = יו (Yu), which in turn are abbreviated forms of the Tetragrammaton; the name of the Lord: YHWH.

The first part of our name is the third person singular (or actually and technically the future form) of the verb סמך (samak), meaning to uphold or support:

🔼Ismachiah meaning

For a meaning of the name Ismachiah, NOBSE Study Bible Name List proposes Yahweh Will Sustain. Jones' Dictionary of Old Testament Proper Names reads Supported Of The Lord. And BDB Theological Dictionary has Yah Sustaineth.